1. Field of the Invention
The present invention relates to a car AC generator and, particularly, to a water-proof structure for slip rings and brushes.
2. Description of the Prior Art
FIG. 8 is a sectional view of a car AC generator equipped with a vacuum pump of the prior art, FIG. 9 is an enlarged sectional view of slip rings 13, brushes 17 and parts therearound shown in FIG. 8, and FIG. 10 is a sectional view cut on line A--A of FIG. 9. In FIG. 8, reference numeral 1 denotes a bracket front and 2 a bracket rear both of which are arranged to face each other to form the outer shell of the generator. Denoted by 3 is a cylindrical stator which consists of a core and a coil and is fastened to the peripheral wall of the bracket front 1 and the peripheral wall of the bracket rear 2 by a bolt 40 in the inside space surrounded by the bracket front 1 and the bracket rear 2 of the outer shell of the generator. Denoted by 4 is a generator shaft which is installed in the center portions of the bracket front 1 and the bracket rear 2 in such a manner that it can rotate by a bearing front 5 and a bearing rear 6. Reference numeral 7 denotes a pulley which is fastened to the generator shaft 4 projecting forward from the bracket front 1 by a nut 8 in such a manner that it can rotate together with the generator shaft 4. Denoted by 9 is a cylindrical rotor which consists of a set of a magnetic pole and a field coil and is fitted in the stator 3 in such a manner that it can rotate together with the generator shaft 4. Denoted by 10 is a fan front which is fixed to the front side of the magnetic pole of the rotor 9 and 11 a fan rear which is fixed to the rear side of the magnetic pole of the rotor 9. Denoted by 12 is a cylindrical slip ring support unit made from a synthetic resin and fixed to the generator shaft 4 between the rotor 9 and the bearing rear 6 in such a manner that it can rotate together with the generator shaft 4. Denoted by 13 is a plurality of annular slip rings which are spaced apart from one another in a direction parallel to the axial direction of the generator shaft 4 and fixed to the outer peripheral surface of the slip ring support unit 12. Denoted by 14 is a packing and 15 a cylindrical slinger unit made from a synthetic resin and fixed to the center portion of the bracket rear 2 through the packing 14 in such a manner that it surrounds the slip ring support unit. Denoted by 16 is a brush holder unit projecting outward from part of the slinger unit 15 and 17 a plurality of brushes which correspond to the number of the slip rings 13 and are inserted into the brush holder unit 16 and whose end portions projecting into the inside of the slinger unit 15 from the brush holder unit 16 are each in contact with the slip rings 13. Denoted by 18 is a brush spring for pressing the plurality of brushes 17 against the slip rings 13 elastically, 42 a regulator which is fixed to the brush holder unit 16, 19 a rectifier which is composed of diodes and the like and fixed to the peripheral wall of the bracket rear 2 outside the slinger unit 15. Denoted by 20 is a slip ring terminal lead wire which projects outward from the slip ring support unit 12, 21 a coil lead wire extending from the field coil of the rotor 9 and connected to the slip ring terminal lead wire 20, 22 is a vacuum pump which is installed outside the bracket rear 2, and 23 a vacuum pump rotor which is mated with the spline unit 24 of the generator shaft 4 projecting backward from the bracket rear 2 in such a manner that it can rotate together with the spline unit 24.
A description is subsequently given of the operation of the car AC generator equipped with a vacuum pump when it is mounted on an automobile. When a driver turns on the ignition switch of the automobile while the AC generator equipped with a vacuum pump is installed outside the cylinder block of an engine and a ring-shaped belt is stretched between a pulley provided on the crank shaft of the engine and the pulley 7 of the car AC generator equipped with a vacuum pump, a current runs through an ignition coil from the battery of the automobile to start the engine and an excitation current runs from the battery to the field coil of the rotor 9 through the regulator 42, the brushes 17 and the slip rings 13. In this state, when the generator shaft 4 turns by the start of the engine and the rotor 9 rotates, 3-phase AC induced electromotive force is generated in the coil of the stator 3, rectified by the rectifier 19 and charged into the battery. By the rotation of the rotor 9, the fan front 10 and the fan rear 11 are rotated and air in the engine room of the automobile is supplied into the inside space of the outer shell of the generator from the inlet port of the bracket front 1 and the inlet port of the bracket rear 2 to cool such parts as the stator 3, the rotor 9, the regulator 42 and the rectifier 19 in the inside space of the outer shell of the generator and is exhausted into the engine room from the outlet port of the bracket front 1 and the outlet port of the bracket rear 2.
In the car AC generator equipped with a vacuum pump of the prior art, as shown in FIG. 9, the space between the bracket rear 2 and the slinger unit 15 is made waterproof by the packing 14. However, since the slinger unit 15 is fixed to the bracket rear 2 and the slip rings 13 turn together with the generator shaft 4, a gap 25 is formed between the slinger unit 15 and the slip ring support unit 12. When water enters the inside space of the outer shell of the generator from the inlet ports, outlet ports and the like of the bracket front 1 and the bracket rear 2, there is a possibility that the water enters the gap 25 from an opening 26 located on the front side (pulley side) of the slinger unit 15. Therefore, a water-proof structure is desired for preventing water entering the gap 25 from the opening 26 from reaching contact portions between the slip rings 13 and the brushes 17. However, a labyrinth 27 defined by the inner peripheral surface of the slinger unit 15 and the outer peripheral surface of the slip ring support unit 12 has a shape disadvantageous for waterproofing. That is, the inner peripheral surface of the slinger unit 15 is a surface parallel to the generator shaft 4. The outer peripheral surface of the slip ring support unit 12 has an opening side surface 12a parallel to the inner peripheral surface of the slinger unit 15 and a slip ring side surface 12b which falls toward the generator shaft 4 from the opening side surface 12a.
Therefore, since the generator shaft 4 turns during the operation of the generator, water entering from the opening 26 is scattered toward the slinger unit 15 from the opening side surface 12a of the slip ring support unit 12 by centrifugal force, and the scattered water flows down along the inner peripheral surface of the slinger unit 15 as shown by an arrow X1 in FIG. 10, goes over a brush seat 28 which is provided inside the brush holder unit 16 to surround the brushes 17 from the inner peripheral surface of the slinger unit 15 and reaches the brushes 17. Therefore, there is a possibility that water flows into the gap between the brushes 17 and the brush seat 28.
Although the generator shaft 4 stops turning during the suspension of the generator, when water flows into the slip ring side surface 12b from the opening side surface 12a of the slip ring support unit 12 through the opening 26 by vibration transmitted to the AC generator equipped with a vacuum pump from the automobile, there is a possibility that the water flows down along the slip ring side surface 12b as shown by an arrow X2 in FIG. 10 and runs into the contact portions between the slip rings 13 and the brushes 17.
Car AC generators are divided into car AC generators equipped with a vacuum pump and car AC generators without a vacuum pump. It is very common that as many parts as possible are shared by these two different types of car AC generators to reduce costs. Describing this point, as shown in FIG. 8, in a car AC generator equipped with a vacuum pump, to ensure connection between the vacuum pump rotor 23 and the generator shaft 4, the diameter of the spline unit 24 is made large. As for the assembly procedure of parts to the generator shaft 4, the rotor 9 is press fitted onto the generator shaft 4 from the front side using such an apparatus as a press. Using such an apparatus as a press, the slip ring support unit 12 including the slip rings 13 and the slip ring terminal lead wire 20 is press fitted onto the generator shaft 4 from the rear side. After the coil lead wire 21 of the rotor 9 is connected to the slip ring terminal lead wire 20 in this state, the fan front 10 and the fan rear 11 are welded to the core of the rotor 9. According to this assembly procedure of parts, the fan front 10 and the fan rear 11 are prevented from being crushed by the press fitting tool of the press and the fan rear 11 can hold the intermediate portion of the coil lead wire 21 at an accurate position. However, since a clearance L2 between the inner diameter of the fan rear 11 and the outer diameter of the slip ring support unit 12 and a clearance L1 in a radial direction between the coil lead wire 21 of the fan rear 11 and the slip ring terminal lead wire 20 must be made large, the diameters of the generator shaft 4, the bearing rear 6, the slip ring support unit 12, the slip rings 13 and the slinger unit 15 are larger than those of a car AC generator without a vacuum pump.
FIG. 11 is an enlarged sectional view of slip rings 131, brushes 17 and parts therearound of a car AC generator without a vacuum pump of the prior art. In FIG. 11, common parts are given the same reference numerals as those of the above car AC generator equipped with a vacuum pump and non-common parts are given different reference numerals. The front portion of a slip ring support unit 121 fitted onto a generator shaft 41 covers the opening 26 of a slinger unit 152 from inside to outside, and a labyrinth 271 is formed to have a U-shaped section and opened in a circumferential direction by the outer annular projection 29 of the slinger unit 152 and the opening 30 of the slip ring support unit 121. Therefore, unlike the car AC generator equipped with a vacuum pump, in the car AC generator without a vacuum pump, water hardly enters the labyrinth 271 but there is a possibility that water entering the labyrinth 271 flows into the gap between the brushes 17 and the brush seat 28 as described above and also flows into the contact portions between the slip rings 131 and the brushes 17 during both of the operation and suspension of the generator.
Since the fan rear 11 is shared by the car AC generator equipped with a vacuum pump and the car AC generator without a vacuum pump and the slip ring terminal lead wire 20 and the coil lead wire 21 are connected to each other, the clearance L1 of the car AC generator equipped with a vacuum pump must be made the same in size as the clearance L1 of the car AC generator without a vacuum pump (L1=L1). Therefore, the clearance L2 (see FIG. 8) between the inner diameter of the fan rear 11 and the outer diameter of the slip ring support unit 12 of the car AC generator equipped with a vacuum pump becomes much smaller than L2' of the car AC generator without a vacuum pump (see FIG. 11)(L2&lt;L2'). As a result, the labyrinth 27 of the car AC generator equipped with a vacuum pump cannot be made the same in shape as the labyrinth 271 of the car AC generator without a vacuum pump. Reference symbol 2a in FIG. 11 denotes a bracket rear, 61 a bearing rear and 141 a packing.